Process for the preparation of free-flowing, lump-free redispersible, synthetic resin powders

Abstract

This invention relates to a process for the preparation of free-flowing, lump-free redispersible synthetic resin powders by spraydrying aqueous dispersions of synthetic resins containing an added amount of a water-soluble condensation product from melamine, formaldehyde and containing sulfonate groups.

We claim: 
     
       1. A process for the preparation of free-flowing lump-free, water-redispersible synthetic resin powder which consists essentially in spraydrying an aqueous polymerizate dispersion of a water-insoluble synthetic resin having a softening point of between 0°C and 40°C and selected from the group consisting of polymers of acrylic acid esters, copolymers of styrene and acrylic or methacrylic acid esters, copolymers of styrene and butadiene, terpolymers of styrene, butadiene and acrylic acid esters, polymers of vinyl esters, copolymers of vinyl acetate and straight-chain vinyl esters, copolymers of vinyl acetate and branched vinyl esters, .[.polymers of vinyl chloride, polymers of olefins, copolymers of vinyl chloride and olefins, copolymers of vinyl chloride, acrylic acid esters and vinyl acetate.]. .Iadd.copolymers of vinyl esters and vinyl chloride, copolymers of vinyl esters and olefins, terpolymers of vinyl esters, vinyl chloride and olefins, terpolymers of vinyl chloride, acrylic acid esters and vinyl acetate, .Iaddend.and copolymers of vinylidene chloride and acrylic acid esters, and having added thereto from 2% to 30% by weight, based on the solids content of said polymerizate dispersion, of a water-soluble condensation product of melamine and formaldehyde containing sulfonate groups in the molar ratio of melamine:formaldehyde:sulfonate groups of 0.5 to 2:2 to 4:0.5 to 2, under customary spray-drying conditions of exposure to warm gases at temperatures of from 30°C to 50°C and recovering said free-flowing, lump-free, water redispersible synthetic resin powder. 
     
     
       2. The process of claim 1 wherein said water-soluble condensation product is added to said aqueous polymerizate dispersion in an amount of from 5% to 19% by weight, based on the solids content of said polymerizate dispersion. 
     
     
       3. The process of claim 1 wherein said sulfonate groups in said condensation product are alkali metal sulfonate groups. 
     
     
       4. The process of claim 1 wherein said molar ratio of melamine: formaldehyde: sulfonate groups is 1:3:1 and said sulfonate groups are alkali metal sulfonate groups. 
     
     
       5. The process of claim 1 wherein said water-soluble condensation product is the condensation product of one mol of melamine, three mols of formaldehyde and one mol of sodium bisulfite. 
     
     
       6. The product produced by the process of claim 1. 
     
     
       7. A process for improving hydraulic setting masses which consists in adding from 2% to 25% by weight, based on the hydraulic setting ingredients, of the product of claim 6 to a hydraulic setting mass.